The sample code for this example app can be found in this GitHub repository. The example app showcases how to subscribe to webhook notifications and update product inventory across multiple product variants for a gift basket product.

To download the necessary dependencies, navigate to the application folder and type bundle install

Step 1: Exposing your application to the Internet

Your application is going to be receiving requests from Shopify, so it needs to be exposed to the Internet. The simplest way to achieve this is through a tunneling service such as ngrok, which will allow you to create a secure tunnel from the public Internet to your local machine.

If you’re working on OSX or Linux, start ngrok with ./ngrok http 4567. If you’re on Windows, start ngrok with ngrok http 4567.

This will create a tunnel to your local machine on port 4567, which is the default port for Sinatra applications.

Note

If you are running Sinatra on a port that’s not the default (4567), you’ll need to configure ngrok to forward requests to the appropriate port.

Step 2: Configuring your application

Each time you start ngrok, you’ll be assigned a randomly generated subdomain (for example 859998a8.ngrok.io). You will need to configure your application to refer to this address so that Shopify knows where to find your app:

Change the APP_URL parameter so that it matches the subdomain that you’ve been assigned by ngrok. If you’re not using ngrok, this parameter should match the URL where your application is deployed.

In the folder containing the project code, create a new file named .env and open it in a text editor.

Tip

This example application uses the dotenv Ruby gem to allow you to pull your API_KEY and API_SECRET credentials in from an external file. Your .env file is ignored in GitHub by your .gitignore file, so your credentials will not be visible to humans.

Libraries

To start, some useful libraries are included for developing your application:

require'shopify_api'require'sinatra'require'httparty'require'dotenv'

The Shopify API gem allows you to effortlessly make API calls to Shopify. Sinatra is a lightweight web framework for Ruby that you’ll use to quickly develop your web application. You’ll also be using HTTParty to make HTTP requests. As mentioned before, the dotenv gem will allow you to load environment variables from an external configuration file.

Initialization

At the beginning of the class, some constant values are defined as well as the initialize method.

Some constant values are defined to store the application’s API key and secret key, as well as the base URL of the application. (API_KEY, API_SECRET, APP_URL)

The dotenv gem is invoked to import the parameters defined in the .env file that you created.

The application key and secret key are initialized from their respective environment variables.

The empty hash is declared (@tokens), which will be used to store the access tokens granted to the application by Shopify.

Tip

Storing access tokens in memory is a naive approach, and these tokens will be lost forever when the application is restarted. In a production application, you should use a more permanent method of storage such as a relational database.

Installation

Sinatra uses routes to invoke a particular method when a client sends an HTTP request to the specified address.

get'/giftbasket/install'doshop=request.params['shop']scopes="read_orders,read_products,write_products"# construct the installation URL and redirect the merchantinstall_url="http://#{shop}/admin/oauth/authorize?client_id=#{API_KEY}&scope=#{scopes}"\"&redirect_uri=https://#{APP_URL}/giftbasket/auth"redirectinstall_urlend

The first route defined in the application, /giftbasket/install, is used to define the address where the merchant is redirected to when they click Get in the Shopify App Store. This is the address that you defined earlier as the Application URL in the application settings of your partner dashboard.

When the merchant hits this route, you need to redirect them to the application installation screen on Shopify which will look like this:

In the parameters of the install_url, you need to include the following:

The redirect_uri parameter, which is where the merchant will be redirected after they authorize the installation. This should match the URL defined in the partner dashboard as the Redirection URL. In the case, the merchant is redirected to /giftbasket/auth.

Authenticating with Shopify

After the merchant has authorized the installation of your application, you’ll need to authenticate with Shopify using the OAuth protocol. If you’re not familiar with OAuth, please see our documentation on OAuth.

Verify the request

The first step is to verify that the request is indeed coming from Shopify. You will be able to verify this by performing HMAC signature validation.

First, the hmac parameter is removed from the hash. Next, the remaining keys in the hash are sorted lexicographically, and each key and value pair is joined with an ampersand (‘&’). The resulting string is hashed with the SHA256 algorithm using the application’s secret key as the encryption key. The resulting digest is compared against the hmac parameter provided in the request. If the comparison is successful, you can be assured that this is a legitimate request from Shopify.

Get an access token

To make Shopify API calls on a particular shop, you’ll need an access token belonging to that shop.

To get the access token, send a POST request to https://<shop>/admin/oauth/access_token where shop is the domain of the shop where the application is being installed (for example test-shop.myshopify.com). The body of the POST request will contain the API key for the application, the application secret key, as well as the code provided in the original request parameters.

If the request was formed correctly, you should expect to receive a response with status code 200 (OK). This response will contain the access token that you’ll be able to use to instantiate a session with the particular Shopify store that you are trying to access. For the sake of this example, you’ll be storing your access token in a hash where the key is the shop domain.

ifresponse.code==200@tokens[shop]=response['access_token']elsereturn[500,"Something went wrong."]endend

Tip

For the sake of this example, we’ve written our own simple OAuth strategy to illustrate the process. If you’re building a Ruby application outside of this example, we recommend using the omniauth-shopify-oauth2 Ruby gem.

Creating the webhook subscription

After receiving the access token, you can use it to instantiate a session with Shopify. When the session is active, your application can begin making API calls to Shopify.

This example application utilizes Webhooks which allow Shopify to communicate with the application when certain shop events are triggered.

definstantiate_session(shop)# now that the token is available, instantiate a sessionsession=ShopifyAPI::Session.new(shop,@tokens[shop])ShopifyAPI::Base.activate_session(session)enddefcreate_order_webhook# create webhook for order creation if it doesn't existunlessShopifyAPI::Webhook.find(:all).any?webhook={topic: 'orders/create',address: "https://#{APP_URL}/giftbasket/webhook/order_create",format: 'json'}ShopifyAPI::Webhook.create(webhook)endend

In this case, the webhook subscription has the topic orders/create. This means that Shopify will send a POST request to the specified address every time a new order is created on the merchant’s shop.

Receiving and verifying webhooks

When your application receives the POST request to the address you’ve specified, the first thing you need to do is verify that the request is actually from Shopify and not a potential attacker. The HTTP header of every webhook request sent from Shopify contains a HMAC-SHA256 signature generated using the application’s secret key and the data contained in the body of the request. You will need to generate the same signature and compare it against the header value.

Inside the body of the verify_webhook helper function, the SHA256 digest is computed and compared against the digest provided by Shopify in the HTTP_X_SHOPIFY_HMAC_SHA256 header. A value of true or false is returned.

If the comparison was successful, you’ll need to extract the shop name from the request header and look up the access token necessary to activate a session with Shopify.

ifwebhook_okshop=request.env['HTTP_X_SHOPIFY_SHOP_DOMAIN']token=@tokens[shop]unlesstoken.nil?session=ShopifyAPI::Session.new(shop,token)ShopifyAPI::Base.activate_session(session)elsereturn[403,"You're not authorized to perform this action."]endelsereturn[403,"You're not authorized to perform this action."]end

The body of the request will contain the information about the new order in the form of a JSON-encoded Order resource.

Making API calls

When the webhook request is received, the application performs the following actions:

Inspects the line_items property of each order.

Inspects the variant_id property of each line item and then determines if they contain a metafield property with the key ingredients.

If true, the app considers that product variant to be a gift basket. The value of the metafield contains a comma-separated list of variant_ids that belong to the gift basket product (created by the merchant).